Glass fibers have been used in various forms such as chopped filaments and strands, continuous filaments and strands and sundry mats for reinforcing polymeric materials like thermoplastics and thermosetting materials. These glass fibers are produced from molten streams of glass being attenuated from orifices in a bushing of a glass batch melting furnace. After the glass fibers are formed and have cooled somewhat, an aqueous treating composition, known as a sizing composition, is applied to the fibers to provide protection from interfilament abrasion and to make the glass fibers more compatible with the thermoplastic or thermosetting materials they will reinforce. The glass fibers are then chopped, or gathered into strands and chopped, or gathered into strands to form continuous strands. The chopping process, where the fibers or strands or groups of fibers are chopped during forming, is known as a wet chop process. If the continuous glass fiber strands are subsequently chopped, such a process is known as a dry chop process. In addition, continuous glass fiber strands can be manufactured into continuous glass fiber strand mat. Also, chopped glass fiber strand mat can be produced. All of these glass fiber products are useful in reinforcing thermoplastic and thermosetting polymeric materials to increase the strength and other properties of the polymeric materials.
Thermoplastics are reinforced by incorporating reinforcement such as glass fibers into the thermoplastic polymer matrix. Glass fibers for use in such reinforcements originally consisted of a polymer coated glass fiber roving that was chopped into pellets. The pellets, known as "long glass" products were about 1/8 inch in diameter and about 1/4 to 1/2 inch in length. The development of "short glass" products, where the chopped glass fiber strand is produced by dry chopping sized glass fiber strand roving or producing wet chopped glass fiber strand, involves lengths of the chopped glass fiber strands from around 1/8 to 1/4 of an inch. These short glass products have allowed for the production of reinforced thermoplastics by extrusion blending of a mixture of resin and chopped glass fibers. Reinforced thermoplastics can be prepared to contain glass fibers in levels ranging from about 10 to 55 percent on a weight basis. With short glass products, it is possible to achieve the desired glass content by blending moldable thermoplastic polymer containing glass fibers with a non-reinforced moldable thermoplastic polymer. For example, a fiber glass reinforced polymer concentrate having a glass content of 40 percent by weight or greater can be blended with unreinforced polymer to achieve the desired reduced level of glass reinforcement in the blended moldable product. Thermoplastic resins that are useful in producing reinforced thermoplastic products include such polymers as polyamides, polystyrenes, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene terpolymers, polycarbonates, polypropylenes, polyethylenes, polyacetals, polysulfones, polyurethanes, polyphenylene-oxides, and thermoplastic polymers like polybutylene terephthalates and polyethylene terephthalates.
The glass fiber strands that have been used in producing short glass for polymeric reinforcement are coated by applying a treating or sizing composition to the glass fibers as they are formed. This sizing composition usually contains a lubricant, a coupling agent, and a film forming polymer such as poly(vinyl acetate). The selection of these types of components for the sizing component can be crucial to the properties of the resultant glass fiber reinforced polymer. For example, it is known in the art that the proper selection of a coupling agent has a significant effect on the properties of resultant reinforced thermoplastics.
In the production of high performance polymeric materials, in addition to characteristics obtained as a result of the high performance properties of the polymer, these materials would be expected to have good strength properties because of the presence of the glass fibers. For instance, in reinforcing high performance thermoplastic polymers, it would be expected to achieve a high performance reinforced polymeric material with good tensile and impact strength so that the resultant properties of the high performance polymer can be used most advantageously. One such high performance polymer is polycarbonate which is a polyester of carbonic acid. Glass fibers have been used to reinforce polycarbonate at levels of reinforcement in the range of 10-40% glass fibers. It has been reported in Modern Plastics, Volume 43 at page 102, that polycarbonate resin reinforced with short glass fiber strand at a 20% glass content gives a tensile strength at 73.degree. F. (23.degree. C.) of 12,000-18,500 PSI (827-1276 Bars), an elongation at 73.degree. F. (23.degree. C.) of 2.5-3.0%, a flexural strength at 73.degree. F. (23.degree. C.) of 17,000-25,000 PSI (1172-1724 Bars), and an Izod impact strength at 73.degree. F. (23.degree. C.) of 1.5-2.5 foot pounds/inch (78-134 joule/meter).
It would be advantageous to have glass fiber strands sized with a sizing composition that adequately protects the strands from interfilament abrasion and yields reinforced polymeric resin material with high tensile strength, flexural strength, and impact strength. Such a sized glass fiber strand would be especially desirable for use in high performance polymers such as the polycarbonate thermoplastic polymer so that the high performance properties of the polycarbonate polymer can be utilized most efficiently to achieve high performance properties in the molded reinforced polycarbonate material.
Such achievements can be made while also achieving ease of processability of the glass fibers in producing glass fibers in their various forms and in producing the reinforced polymeric material, such as by compression molding, injection molding, and the like.
It is an object of the present invention to provide an aqueous sizing composition for glass fibers and to provide the sized glass fibers that yield reinforced polymeric materials having properties such as tensile strength, flexural strength, and impact strengths at the upper end of or greater than the range of these strengths as aforedescribed.